This invention relates to methods for positioning a small internal portion of a body at a predetermined point relative to an extracorporeal referent. In an important aspect, the invention is concerned with positioning a small internal body portion detectable by penetrating radiation, such as a concretion within the body of a living human patient, at a predetermined point relative to an external energy source or the like, e.g. for treatment of the body portion with focused or directional wave energy from the source.
One specific application of the invention, which will be particularly considered herein for purposes of illustration, is in the treatment of kidney stones by extracorporeal shock wave lithotripsy (ESWL). Apparatus and procedures for ESWL treatments are described, for example, in U.S. Pat. No. 3,942,531, No. 4,530,358, and No. 4,539,989, and in Ch. Chaussy et al., Extracorporeal Shock Wave Lithotripsy (Basel: Karger, 1982), the disclosures of all of which are herein incorporated by this reference.
Typical ESWL apparatus includes a water-filled shock wave focusing chamber in the form of a partial ellipsoid, truncated orthogonally to the major axis, mounted on (and opening into) a patient-receiving water tank, and so arranged that the first focus of the ellipsoid is within the focusing chamber while the second focus of the ellipsoid is outside the focusing chamber but within the tank. Means such as an arc discharge device are provided for generating high energy shock waves at the first focus of the ellipsoid. The patient to be treated is suspended in the tank on a cradle movably carried by a gantry. With the patient so positioned that the kidney stone to be treated is located at the second focus of the ellipsoid, reflected shock waves generated in the focusing chamber (and propagating through the chamber and tank water and the patient's body) cause the stone to disintegrate. Thereby, in at least many instances, the patient is ultimately able to pass the stone fragments without surgical intervention.
Precise positioning of the stone at the ellipsoid second focus within the tank is critically important, both to achieve the desired result of stone disintegration by the shock waves and also to minimize the possibility of detrimental effects of the shock waves on other portions of the patient's body. To this end, in current practice, two X-ray image intensifiers (herein sometimes also termed fluoroscopes) are mounted above the tank, pointing downwardly toward the patient position, and are oriented at an angle to each other such that their respective viewing axes converge and intersect at the second focus of the ellipsoid. Each fluoroscope is movable along its viewing axis. The two viewing axes define a plane, oblique to the horizontal, which intersects the patient's body transversely. Two X-ray sources (X-ray tubes) are disposed below the tank, in positions for respectively directing radiation upwardly through the patient to the two fluoroscopes along the aforementioned viewing axes. The outputs of the fluoroscopes are respectively displayed on monitors each having a cathode ray tube provided with crosshairs representing rectangular-coordinate axes perpendicular to (and intersecting at) the associated fluoroscope viewing axis. Thus, an operator viewing these monitors can ascertain the positional relation of a kidney stone (which is imaged by X-radiation distinguishably from surrounding body tissue) to the viewing axes of the two fluoroscopes. Owing to the above-described orientation of the fluoroscopes, the kidney stone is properly positioned at the ellipsoid second focus when, but only when, its image is centered in the crosshairs of both monitors.
Heretofore, patient positioning in ESWL apparatus of the described type has been an essentially manual procedure, in which the operator, observing the monitor screens (after the patient has been lowered into the tank on the gantry cradle), manipulates the gantry controls to move the gantry and patient until the kidney stone image is centered on both monitors. This procedure can be relatively difficult and time-consuming; in particular, it involves undesirably long exposure of the patient to X-radiation, since the kidney stone image must be continuously viewed on the monitors as the patient is moved. Moreover, in some circumstances, the gantry cradle may drag across and damage the focusing chamber while the operator is moving the gantry in accordance with visual observation of the monitor.